I want to be able to do this with assembly, e.g., see what is in each register as I step through the program.
GDB can step through instruction by instruction, and you can easily examine registers.
Learning C with gdb
21–30 of 98 posts
Re: Learning C with gdb
#22This is pretty neat, though I found myself doing similar things in small test files when I was first learning C and printing the results. C compile times suck, but with like a 10 line program or so to toy with a language semantic, it was practically instant (in 2007). But then again I had never used a dynamic language like Ruby/Python before then so I didn't know better. More people should be hopping on this bandwago…
> C compile times suck
Can I ask you what you're comparing with? I can compare with C++, Scala and Go. The first two are horrible in that department when compared with C. Go's compiles are blazingly fast.
Re: Learning C with gdb
#23I want to be able to do this with assembly, e.g., see what is in each register as I step through the program.
like digitalinfinity says info registers should be what your looking for. Here's the docs: http://www.ofb.net/gnu/gdb/gdb_61.html
Re: Learning C with gdb
#24GDB skills are one of those super useful abilities that you just can't find in most CS graduates. I often spend a few days with new C developers just teaching them how to use GDB to find problems. They are amazed when they find out you can examine variables and set conditional breakpoints.
This is an area where many college professors fall short. In my intro to CS class we learned C, and the professor explicitly told us to debug our code with printf statements. It wasn't until my first job that I even found out about gdb. I can't believe how much time I wasted trying to debug C and C++ code in college with nothing more than printf and cout.
Re: Learning C with gdb
#25This is pretty neat, though I found myself doing similar things in small test files when I was first learning C and printing the results. C compile times suck, but with like a 10 line program or so to toy with a language semantic, it was practically instant (in 2007). But then again I had never used a dynamic language like Ruby/Python before then so I didn't know better. More people should be hopping on this bandwago…
> C compile times suck Can I ask you what you're comparing with? I can compare with C++, Scala and Go. The first two are horrible in that department when compared with C. Go's compiles are blazingly fast.
I'm not really comparing it to anything, just speaking from experience of having waited many hours waiting for C programs to compile in the past.
Re: Learning C with gdb
#26GDB skills are one of those super useful abilities that you just can't find in most CS graduates. I often spend a few days with new C developers just teaching them how to use GDB to find problems. They are amazed when they find out you can examine variables and set conditional breakpoints.
This is an area where many college professors fall short. In my intro to CS class we learned C, and the professor explicitly told us to debug our code with printf statements. It wasn't until my first job that I even found out about gdb. I can't believe how much time I wasted trying to debug C and C++ code in college with nothing more than printf and cout.
What makes it even worse is the lack of a REPL means that between each change you need to recompile. In any large program this is going to take minutes and they add up. A simple GDB invocation is not only a better way of tracking it down, but can potently save hours.
Re: Learning C with gdb
#27While graphical debuggers are great overall, there are times when I prefer to get down to the command line and do my debugging there. And quite surprisingly, I don't lose much efficiency there, either. But then, this could be the story of most command line utilities: Seems fiddly at first, but actually it is quite usable and often times more convenient than all those whiz-bang graphical tools.
The only thing I like about graphical debuggers is the ease of which you can set up multi-window dashboards. I can have my stack windows a few watched variables and the code all on one screen at the same time as I step through the program
Re: Learning C with gdb
#28I want to be able to do this with assembly, e.g., see what is in each register as I step through the program.
GDB can step through instruction by instruction, and you can easily examine registers.
Can I do this with a hand-written assembly program, i.e. not necessarily one that has been compiled with as and subject to GNU default optimisations or "constraints"?
Re: Learning C with gdb
#29for the somewhat-graphically-inclined, gdb mode in emacs has the much under-advertized 'M-x gdb-many-windows' which shows your stack, local variables, breakpoints etc. in separate 'windows'.
Re: Learning C with gdb
#30lldb would be even better for using instead of gdb because lldb actually uses clang's parsing for everything.
I was watching an Apple talk on lldb which explained this in more detail, and it shows a lot of promise for a debugger to have a full C compiler inside of it.